void Student::addPair()
{
    if(pair != NULL) return;
    
    for(int i = 0; i<K; i++)
    {
        Student  * w = welcome[i];
        if(w == NULL || w->pair != NULL) continue;
        for(int j = 0; j<K; j++)
        {
            if(w->welcome[j] == this)
            {
                pair = w;
                w->pair  = this;
                return;
            }
        }
        bool ifNoLove =true;
        for(int j = 0; j<K; j++)
        {
            if(w->welcome[j] != NULL && w->welcome[j]->pair == NULL)
            {
                ifNoLove = false;
                break;
            }
        }
        if(ifNoLove)
        {
            pair = w;
            w->pair = this;
            return;
        }
    }
}
void Student::printPair()
{
    if(pair != NULL)
       cout << name << ":" << pair->name << endl;
}

